thermochemistry Thermochemistry is the study of the heat energy which is associated with chemical reactions and/or phase changes such as melting and boiling. A reaction may release or absorb energy, and a phase change may do the same. Thermochemistry focuses on ...

, the Thomsen–Berthelot principle is a hypothesis in the

history of chemistry The history of chemistry represents a time span from ancient history to the present. By 1000 BC, civilizations used technologies that would eventually form the basis of the various branches of chemistry. Examples include the discovery of fire, e ...

which argued that all chemical changes are accompanied by the production of

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

and that processes which occur will be ones in which the most heat is produced. This principle was formulated in slightly different versions by the Danish chemist

Julius Thomsen The gens Julia (''gēns Iūlia'', ) was one of the most prominent patrician families in ancient Rome. Members of the gens attained the highest dignities of the state in the earliest times of the Republic. The first of the family to obtain t ...

in 1854 and by the French chemist

Marcellin Berthelot Pierre Eugène Marcellin Berthelot (; 25 October 1827 – 18 March 1907) was a French chemist and Republican politician noted for the ThomsenBerthelot principle of thermochemistry. He synthesized many organic compounds from inorganic substa ...

in 1864. This early postulate in classical thermochemistry became the controversial foundation of a research program that would last three decades. This principle came to be associated with what was called the ''thermal theory of affinity'', which postulated that the heat evolved in a

chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...

was the true measure of its affinity. This hypothesis was later disproved, however, when in 1882 the German scientist

Hermann von Helmholtz Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Associat ...

proved that affinity was not given by the heat evolved in a chemical reaction but rather by the maximum work, or free energy, produced when the reaction was carried out reversibly.

References

See also